As known the quality of water depends on its physical, chemical and biological properties. Preservation of water quality and adequate purification of sewage effluent has become a central problem of environmental protection in recent years.
The various technologies of the water and sewage purification include physical, chemical and biological processes. In a version of the biological processes so-called drip bodies are used as the primary purification phase of mainly multiphase sewage water purification technologies. Their application permits active sludge biological purification technology to be carried out at higher efficiency.
The packing of the biological drip bodies can consist of various materials although nearly exclusively plastic packings are used today. The packings are arranged on top of one another, built up as tower or column to form the drip bodies, a water distributor being provided at the top of the column.
According to the principle of operation of the biological drip bodies the waste or sewage water flows down intermittently or continuously along the bilogical film developing on the surface of packings. This brings about coagulation and absorption of the pollutant, in the course of which the microorganic culture forming the biological film dissolves solutes of water to be for deriving energy and cell synthesis. The overmultiplied biological film fractions agglomerate in a sedimentator, the cell-free enzyme activity of the microorganisms being decomposed to materials which diffuse through the cell wall and thus participlate in the metabolism process.
The oxygen required for biochemical oxidation is supplied by the air passing through the packing. Flowing down in the drip body the BOD.sub.5 value of the waste waters diminishes exponentially.
Thus the packings used in the biological drip bodies must meet several requirements:
The surface area related to unit volume of the packings covered by the biological film has to be as large as possible. At the same time the void volume also must be large in the packing to have sufficient free cross section for the filmy downflow of the waste water and adequate oxygen supply should be available.
In addition, the packing must be resistant to chemical, biological and physical effects and must possess adequate static strength in order to be able to carry the weight of water, the biological film and several packing units arranged on each other.
Further obvious requirements are the easy, simple and fast production of the packings, as well as their fast and simple assembly in columns, operation and maintenance.
One of the most familiar attempts to provided such packings is described in the U.K. patent documents Nos. 1 065 612 and 1 080 991. The elements are plastic sheets with straight or curved generatrix and accordion-like corrugated surfaces. These are generally arranged alternately with flat sheets so that the elements are turned opposite each other.
The fundamental shortcoming of the construction is that as a result of using flat sheets to increase the mechanical strength, the specific surface is relatively small 85 m.sup.2 /m.sup.3 which results in poor efficiency.
This technique is also used where the packing consists of sheets corrugated in strips and the sheets are provided with reticular reinforcing elements on the top and bottom. There is no closed channel system and though its specific surface is larger than that of the earlier mentioned solutions, the mechanical loadability of the packing is low.
In the German Federal Republic Patent No. 1 299 665 a packing is described, which consists similarly of sheets folded as an accordion. Corrugations of the adjacent sheets intersect each other and the sheets are made of a moisture absorbing material. The specific surface of the elements is relaively small, the mechanical strength is low, and they are unsuitable for use in biological drip bodies.
It is also known (German Democratic Republic Patent No. 58 104) which consists of trapezoid corrugated sheets. Flat sheets are arranged between corrugated sheets with oblong slots on the corrugated sheets. The specific surface is small, mechanical strength is poor, field of application is mainly contact of liquid and gas.
The plastic packing described in the Hungarian Patent No. 172 169 represents definite progress compared to the earlier systems. This packing is provided with corrugated through channels separated from each other, where the channels are regular hexagon cross sections in any horizontal section of at least one part of the packing. The longitudinal axes of the channels in the vertical plane consist of opposite sections following each other at least in part, and preferably two adjacent sides of each channel are provided with corrugations in cross direction to the longitudinal axis.
This construction enables an increase in the specific surface to 135 m.sup.2 /m.sup.3 and yields very good results. However it has two fundamental drawbacks: the sheets forming the packing are assembled with the use of adhesive. This is expensive, for it requires filler material and further aids; the gluing technology entails the risk of accident, since the applied solvents are poisonous and represent gas and explosion hazard.
A further drawback is that the longitudinal axes of the channels are at a relatively large angle to the vertical (30.degree.-50.degree.). Thus--as a result of gravity--the water tends to flow on the lower part of the channels during operation. This means that mainly in case of heavy surface load the surface participating in intensive purification may be reduced to 50% of the total surface. Hence operation of these packing units is flexible against change of load only in a relatively narrow range.
Clogging, inundation or other failures of the packing requiring repair, maintenance frequently occur even during the most careful operation of the biological drip bodies. Jointing the sheets with adhesive is unfavorable in this respect too, for the sheets cannot be separately replaced, and cleaning or maintenance are difficult.